1. Field of the Invention
The present invention relates to a gas-flow measuring apparatus which is, used, for example, for measuring the flow rate of engine intake air.
2. Description of the Prior Art
Generally, in an internal combustion engine, the amount of intake air is one of the most important driving parameters for controlling the base fuel injection amount, base ignition timing, and the like. A gas-flow measuring apparatus, i.e., an airflow meter, is provided for this purpose. One of the more common prior art airflow meters is the hot-wire type. For example, the hot-wire-type airflow meter may consist of an electric heater provided in an intake-air passage of an engine, and temperature-dependent resistors arranged before and after the electric heater, the electric heater and the temperature-dependent resistors being made of plantinum wires of the same characteristics. In this type of airflow meter, however, the hot-wires are easily broken due to vibration, shock, and the like.
Another airflow meter more resistant to vibration, shock, and the like uses resistance patterns formed on an insulator such as a ceramic substrate. In this case, the resistance patterns are formed by printing. There are, however, limits as to the fineness of resistance patterns obtainable by printing, therefore it is impossible to reduce the size of the patterns beyond a certain point. This airflow meter is consequently somewhat large and has a large heat capacity, thereby reducing the response characteristics.